Direct injection diesel motor with tumble-supported combustion process

ABSTRACT

The process relates to a diesel engine, the individual cylinders ( 1 ) of which are respectively provided with a fuel injection device, having an injector ( 21 ) that discharges into the combustion chamber ( 2 ) of the cylinder ( 1 ), said cylinders comprising at least one discharge valve ( 9 ) and at least one admission valve ( 7 ) for each cylinder, to which are assigned respectively extending admission channels ( 6, 8 ) in the cylinder head ( 3 ), which channels empty at a slant into the combustion chamber ( 2 ), wherein the combustion chamber ( 2 ) of a cylinder ( 1 ) that is limited by the cylinder head ( 3 ) on the one side and the piston bottom ( 13 ) on the other side is designed such that the charge movement inside the combustion chamber ( 2 ) is a rotational movement around the cylinder axis ( 17 ), having a value CU/CA≦0.5 and a tumble movement around the lateral axis having a value of CT/CA≧0.5, and wherein the injector is provided with at least one injector opening.

DESCRIPTION

In addition to a reduction in the fuel consumption, direct-injectiondiesel engines must meet the requirement of a reduction in emissions.For this, it is very important to provide the longest possible, clearinjection distance for the diesel fuel jet and to avoid, if possible,any fuel hitting the cylinder walls, so as to obtain the most uniformfuel-air-mixture.

For a proper processing of the mixture, European Patent A-0 634 572, forexample, discloses that given an essentially level limiting surface ofthe combustion chamber near the cylinder head, the admission channelsmust be installed such that the air flowing into the cylinder will beprovided with a strong rotational movement around the cylinder axis,which is still in effective during the injection of fuel. However, thiscan be achieved only with a geometrically complicated cylinder head.

German Patent A-4 241 104 discloses a diesel engine, for which thecombustion chamber of the cylinder is offset, meaning it has two stageson the cylinder head side that are height-displaced relative to eachother. In that case, the admission valve opens up into the surface ofthe upper stage and the discharge valve issues from the lower stagesurface, respectively with the associated channels for conducting gas.The piston bottom has a corresponding design with stages. The respectivetransition region from one stage to the other is provided at thecylinder head as well as at the piston bottom with an undercut, so thatan essentially cylindrical combustion chamber space forms if the pistonis in the upper dead center position, which extends crosswise to thecylinder axis. The injector discharges in axial direction of thecombustion chamber into this combustion chamber space, that is to saycrosswise to the cylinder axis. This structural design also requires acomplicated design for the cylinder head and a complicated pistondesign.

German Patent A-19 537 028 discloses a diesel engine that is modifiedrelative to German Patent A-4 241 104. The admission valves for thisengine are again arranged higher than the discharge valves, but thelimiting surface of the combustion chamber on the cylinder-head side isslanted on the intake side, as compared to the cylinder axis, andextends horizontally on the discharge side. The associated piston bottomhas a corresponding outline, wherein the essentially horizontal pistonbottom surface that is coordinated with the discharge side extends intothe intake region. Thus, a cylindrical combustion chamber space iscreated in the upper dead center position, which extends crosswise tothe cylinder axis and into which fuel is injected crosswise to thecylinder axis. This combustion chamber design also requiresgeometrically complicated cylinder heads and pistons with a fissuredpiston bottom design.

Thus, it is the object of the invention to create a direct-injectiondiesel engine, effecting a diesel combustion method that permits highcenter pressures with a very favorable fuel consumption and lowemissions, owing to its combustion chamber design.

This object is solved with a diesel engine having individual cylindersthat are respectively provided with a fuel injection device, for whichthe injector discharges into the combustion chamber of the cylinder,said cylinders having at least one discharge valve and at least oneadmission valve for each cylinder, to which are assigned respectivelyextending channels in the cylinder head. These channels empty at a slantinto the combustion chamber, wherein the combustion chamber is limitedby the cylinder head on one side and the piston bottom on the other sideand is designed such that the charge movement inside the combustionchamber is a rotational movement around the cylinder axis, with a valueof CU/CA≦0.5 and a tumble movement around the lateral axis with a valueof CT/CA≧0.5, wherein the injector is provided with at least oneinjection opening. CU refers to the circumferential speed component fora rotational flow and CA correspondingly refers to the axial speedcomponent, so that the ratio CU/CA represents a measure for theintensity of a rotational flow. Analogous to the rotational flow, CTprovides the tangential speed component of the tumble or rollturbulence, whereas CA reflects the axial speed component. The ratioCT/CA represents the measure for the intensity of the tumble flow. Thedevice described in German Patent A-41 33 277, for example, can be usedfor measuring the tumble flow.

By designing the combustion chamber in this way, together with aseparation of the fuel to be injected into a plurality of individualjets, it is possible to produce an optimum mixture inside the combustionchamber, resulting for the most part in a homogeneous fuel-air-mixture.It is particularly useful in this connection if the fuel is injectedinto the combustion chamber with an extremely high pressure, such as canbe realized with the aid of so-called common-rail injection systems andpressures exceeding 1000 bar. In particular the intake configuration isembodied with two essentially parallel extending admission channels thatdischarge at a slant into the combustion chamber, so that thehomogeneous mixture for a direct-injection diesel engine is achievedthrough a so-called tumble movement. The combustion chamber limitingsurface on the cylinder head side can have a level design, at least inpart, such as is known from classic diesel engine designs. The achieved,induced center pressures are in the range of 12 to 14 bar for arotational speed of 1500 RPM, for example, and in the range of 15 to 18bar for 2000 RPM, as well as in the range of 10 to 13 bar for 4000 RPM.

One embodiment of the invention provides that the combustion chamberlimiting surface on the cylinder-head side has a roof-shaped design, atleast in its essential region, wherein at least one admission channelfeeds into one roof surface and at least one discharge channel issuesfrom the other roof surface. It is particularly favorable in this caseif the roof-shaped limiting region is respectively level in the areaadjacent to the “eaves region” of the roof. The piston bottom isdesigned to match the combustion chamber limiting surface on thecylinder-head side. It has turned out that this combustion chamberdesign, which is derived from Otto engines and adapted to the dieselmethod, also results in excellent values for the diesel method withrespect to output, fuel consumption and low emissions, provided theaforementioned conditions of CU/CA≦0.5 and CT/CA≧0.5 are observed forthe charge movement.

One advantageous embodiment of the invention furthermore provides thatthe piston bottom contains an indentation, preferably a pot-shapedindentation. For this, it is useful if the indentation has anessentially circular-cylindrical shape and a level bottom surface. Witha partially roof-shaped piston bottom design, the indentation isarranged in the region of the cylinder axis, so that only the remainingouter edge regions have a roof-shaped design. A level limiting surfacetoward the cylinder wall is provided adjacent to the “eaves region” ofthe roof, in accordance with the outline of the limiting surface on thecylinder head side.

One advantageous embodiment of the invention provides that the verticalaxis of the indentation coincides with the vertical axis of theinjection device, wherein it is particularly advantageous that thevertical axis of the injection device is arranged at a distance andoffset in the direction of the discharge valve.

The invention is explained in further detail with the aid of schematicdrawings of exemplary embodiments, showing in:

FIG. 1 a vertical section through a cylinder;

FIG. 2 a vertical section through the upper region of a piston, alongthe cylinder axis;

FIG. 3 an associated view from above of the piston according to FIG. 2;

FIG. 4 a rotational flow that has formed at the end of the intake phase;

FIG. 5 a tumble flow that has formed;

FIG. 6 schematically the development of a tumble flow in the intakephase;

FIG. 7 the arrangement of injector openings for an injector;

FIG. 8 a modified arrangement for the injector openings;

FIG. 9 an arrangement of injector openings where the openings are atdifferent distances to each other.

FIG. 1 shows a vertical section of a cylinder 1 for a diesel engine, forwhich the combustion chamber 2 is limited by a cylinder head 3 on theone side and a piston 4 on the other side. The limiting surface 5 ofcombustion chamber 2 in the cylinder head 3 is designed in the shape ofa roof for the exemplary embodiment shown herein, wherein one or alsotwo parallel extending admission channels 6 empty side-by-side into theone roof surface 5.1, which admission channels can respectively beclosed off by an admission valve 7. One or two parallel dischargechannels 8 issue from the other roof surface 5.2 and can be closed offrespectively by a discharge valve 9. In the “eaves region” 10 of the tworoof surfaces 5.1 and 5.2, the limiting surface on the cylinder-headside changes to a level edge surface 11 for the exemplary embodimentshown herein, which extends parallel to the ridge line 12 of thelimiting surface 5. However, it is also possible to have an embodimentfor which the roof surfaces at the combustion chamber top as well as atthe piston bottom are formed such that they are tapered toward thecylinder walls.

The angle between admission valve 7 and discharge valve 9 can measure upto 40°, wherein the bisecting line of the angle can be slanted by up to8°, relative to the cylinder axis 17.

The sectional view shown in FIG. 1 is offset in the cylinder head region3, as a result of axis 6.1 for an admission channel 6 and the associateddischarge channel 8. In the region of combustion chamber 2, up to andincluding the piston, the section extends in one plane along thecylinder axis 17.

The piston bottom 13 of piston 4 for the exemplary embodiment shown inFIG. 1 is essentially realized to match the shape of the limitingsurface 5 on the cylinder-head side, with the exception that apot-shaped indentation 14 is worked into the roof surface of pistonbottom 13, as can be seen in FIG. 3. Respectively in the “eaves region”10 of the roof outline, the piston bottom 13 is provided with horizontalsurfaces 16 that match the limiting surfaces on the cylinder-head side.An injection device is arranged in the cylinder head 3, in the region ofcylinder axis 17, which is indicated herein only by its axis 18. Withthe exemplary embodiment shown herein, the injection axis 18 is arrangedoffset by a small measure in the direction toward the discharge channels8. However, it can also coincide with the cylinder axis 17. Depending onthe design and alignment of the injectors, the injection axis can bearranged at a slant of up to 30° relative to the cylinder axis 17.

FIG. 1 shows the piston 4 during its downward movement, while theadmission valves 7 are opened. As a result of the combustion chamberconfiguration and the parallel admission channels 6, which essentiallyempty at an angle α into the combustion chamber 2, a tumble flow formsin the combustion chamber 2 that is indicated with the two double arrows19. This tumble flow is for the most part also maintained during thecompression phase, meaning while the admission valves 7 are closed andthe piston 4 is moving upward. The fuel is then injected just prior tothe end of the compression lift directly into the combustion chamber 2and into this tumble flow, which rotates around a lateral axis thatextends perpendicular to the cylinder axis 17. Since the injectorcontains at least five injector openings, the necessary fuel amount isinjected finely distributed into this tumble flow, so that the fuel cantravel a long distance without making contact with the cylinder walland, in the process, a homogeneous mixture can form in the combustionchamber.

The tumble flow, which is for the most part generated by the geometry ofthe admission channels, is essentially stabilized by the geometry of thecombustion chamber 2, in particular the shape of the limiting surfacesof the roof on the cylinder-head side and the associated shape of thepiston bottom 13 during the compression operation. The indentation 14 inthe piston bottom 13 in this case ensures the desired long distances forthe injected fuel amounts, in addition to also exerting a stabilizingeffect on the tumble. The ratio of indentation diameter to pistondiameter should advantageously be 0.5 to 1.0.

The piston bottom for a modified version can be designed in the shape ofa roof and without indentation, as well as with an optional flattenedsection in the ridge region. A totally flat piston bottom, as shown inFIG. 6, is also conceivable.

The aforementioned asymmetric design of the combustion chamber can beseen in the sectional view as well as the view from above of the pistonbottom embodied in FIGS. 2 and 3. By assigning the reference numbers ofthe individual features previously explained in connection with FIG. 1,it is possible to refer to the preceding description.

FIGS. 2 and 3 show that the pot-shaped indentation 14 in the pistonbottom 13 is essentially circular-cylindrical and has a level bottomsurface 20.

Relative to the horizontal line, the angle of inclination b for theroof-shaped limiting surface is between 13° and 18° and preferablyapproximately 15°, as measured on the side of the cylinder head as wellas on the side of the piston bottom. In the region directly in front ofthe curved transition to the intake opening 7.1, which can be closed offwith the admission valve 7, the admission channels 6 are inclined withtheir center axis 6.1 by an angle α of between 15° and 45°, preferablyabout 30°, relative to the horizontal line.

For a better understanding of the flow conditions, FIG. 4 shows arotational flow that has formed at the end of an intake phase. Theassociated speed components CU and CA are respectively marked witharrows.

FIG. 5 shows a tumble flow that has formed for the same piston position.The speed components CT and CA in this case are also markedcorrespondingly with arrows. FIG. 5 demonstrates that the arrangement ofindentation 14 in the piston bottom 13 contributes considerably tomaintaining the tumble flow during the subsequent upward movement of thepiston 4 in the compression phase. Thus, a sufficient flow component CTis still present during the injection phase, which then ensures that acomplete mixture is formed.

The individual steps from left to right in FIG. 6 show how during theintake phase, meaning when the piston moves downward, the initiallyaxial inflow of air changes to a tumble flow during the further courseof the intake phase until the end of the intake phase. This tumble flowis supported to a high degree by the geometric coordination betweenadmission channels 6 and the cylinder chamber and also by thearrangement of a corresponding combustion chamber roof 5.

FIG. 7 contains a schematic drawing of injector 21 for the fuelinjection device, which projects into the combustion chamber 2. As canbe seen in the drawing, the injector 21 comprises a plurality ofinjector openings 22, but at least five. Relative to the injection axis18, the injector openings are aligned such that the exiting, finelydistributed fuel jets are discharged at an angle c of approximately 45to 80° into the combustion chamber 2.

The above-presented and described combustion chamber design is know perse from Otto engines. Surprisingly, it has turned out that such acombustion chamber design can also meet the requirement for high centerpressures with very favorable fuel consumption and low emissions, evenfor diesel combustion processes with direct injection. In addition, thisinvolves production technological advantages since it is now possible tomanufacture cylinder heads for Otto engines as well as for dieselengines on the same production lines.

The injection device can be provided with injectors, for which thedesign and arrangement of the openings vary. In addition to a so-calledthrottle injector with only one injector opening, injectors having atleast three openings can also be used. The angle c of the individualinjector openings 22, relative to the individual axes 18 of theinjection device, as well as the angle d or the spacing of theindividual injector openings 22 in circumferential direction canrespectively be different. This is shown schematically in FIGS. 6 and 9for a injector with six injector openings 22.1 to 22.6.

What is claimed is:
 1. A diesel engine comprising a plurality of enginecylinders each having a cylinder axis; a cylinder head covering theengine cylinders; at least one intake port opening into each saidcylinder at an oblique orientation to the cylinder axis; said intakeport being provided in said cylinder head; a separate intake valve foropening and closing each said intake port; at least one exhaust portopening into each said cylinder; said exhaust port being provided insaid cylinder head; an exhaust valve for opening and closing saidexhaust port; a fuel injection nozzle opening into each cylinder andhaving a nozzle axis codirectional with said cylinder axis; said nozzlehaving a plurality of outlet openings oriented at an angle of between60° and 80° to said nozzle axis; a piston received for reciprocation ineach said cylinder and having a piston bottom; a combustion chamberdefined in each said cylinder and being bordered by said cylinder headand said piston crown; said cylinder head having wall portions withplanar parts oriented perpendicularly to said cylinder axis andbordering said combustion chamber; said cylinder head having furtherwall portions bordering said combustion chamber and being formed by afirst and a second surface inclined towards one another in an invertedV-shaped configuration; said intake ports terminating in said firstsurface and said exhaust port terminating in said second surface; saidpiston bottom having an inverted V-shaped configuration complemental tothe inverted V-shaped configuration of said cylinder head; whereby acombustion charge introduced into said cylinder propagates as a twistflow about said cylinder axis and as a tumble flow about an axistransverse to said cylinder axis such that CU/CA≦0.5 and CT/CA≧0.5,wherein CU is the circumferential velocity component of said twist flow,CA is the axial velocity component of said twist flow and CT is thetangential velocity component of said tumble flow.
 2. A diesel enginecomprising (a) a plurality of engine cylinders each having a cylinderaxis; (b) a cylinder head covering the engine cylinders; (c) at leastone intake port opening into each said cylinder at an obliqueorientation to the cylinder axis; said intake port being provided insaid cylinder head; (d) a separate intake valve for opening and closingeach said intake port; (e) at least one exhaust port opening into eachsaid cylinder; said exhaust port being provided in said cylinder head;(f) an exhaust valve for opening and closing said exhaust port; (g) afuel injection nozzle opening into each cylinder; said nozzle having atleast one outlet opening; (h) a piston received for reciprocation ineach said cylinder; said piston having a piston bottom; (i) a combustionchamber defined in each said cylinder and being bordered by saidcylinder head and said piston crown; said combustion chamber includingmeans for effecting propagation of a combustion charge, introduced intosaid cylinder, as a twist flow about said cylinder axis and as a tumbleflow about an axis transverse to said cylinder axis such that CU/CA≦0.5and CT/CA≧0.5, wherein CU is the circumferential velocity component ofsaid twist flow, CA is the axial velocity component of said twist flowand CT is the tangential velocity component of said tumble flow.
 3. Thediesel engine as defined in claim 2, wherein said fuel injection nozzlehas a nozzle axis codirectional with said cylinder axis.
 4. The dieselengine as defined in claim 3, wherein said fuel injection nozzle hasmore than one outlet opening; and further wherein said outlet openingsof said nozzle are oriented at an angle of between 60° and 80° to saidnozzle axis.
 5. The diesel engine as defined in claim 2, wherein wallportions of said cylinder head bordering said combustion chamber haveplanar parts.
 6. The diesel engine as defined in claim 5, wherein saidplanar parts are oriented perpendicularly to said cylinder axis.
 7. Thediesel engine as defined in claim 2, wherein wall portions of saidcylinder head bordering said combustion chamber are formed by a firstand a second surface inclined towards one another in an invertedV-shaped configuration; said intake ports terminating in said firstsurface and said exhaust port terminating in said second surface.
 8. Thediesel engine as defined in claim 2, wherein said piston bottom has aninverted V-shaped configuration complemental to the inverted V-shapedconfiguration of said cylinder head.
 9. The diesel engine as defined inclaim 2, wherein said piston bottom has an indentation.
 10. The dieselengine as defined in claim 9, wherein said indentation is dish-shaped.11. The diesel engine as defined in claim 9, wherein said indentationhas an essentially circular-cylindrical shape.
 12. The diesel engine asdefined in claim 9, wherein said indentation has a level bottom surface.13. A diesel engine as defined in claim 9, wherein said indentation hasan indentation axis extending along said cylinder axis and saidinjection nozzle has an axis coinciding with an axis of said injectionnozzle.
 14. The diesel engine as defined in claim 9 wherein saidindentation has an axis which is offset relative to said nozzle axistoward said exhaust valve.